Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
In a modern magnetic hard disk drive device, each head is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit. The plurality of HGAs are attached to various arms of the actuator.
Modern laminated flexures typically include conductive copper traces that are isolated from a stainless steel structural layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flexible printed circuit (FPC) on the actuator body, each suspension assembly includes a flexure tail that extends away from the head along a corresponding actuator arm and ultimately attaches to the FPC adjacent the actuator body. That is, the flexure includes traces that extend from adjacent the head and continue along the flexure tail to a plurality of flexure bond pads for electrical connection to the FPC. The FPC includes conductive electrical traces that terminate in a plurality of FPC bond pads that correspond to and are electrically connected to the flexure bond pads.
To facilitate electrical connection of the conductive traces of the flexure tails to the conductive electrical terminals of the FPC during the HSA manufacturing process, the flexure tails must first be properly positioned relative to the FPC so that the flexure bond pads are aligned with the FPC bond pads. Then the flexure tails must be held or constrained against the FPC bond pads while the aforementioned electrical connections are made, e.g., by ultrasonic bonding, solder jet bonding, solder bump reflow, or anisotropic conductive film (ACF) bonding.
An anisotropic conductive film is typically an adhesive doped with conductive beads of similar size or diameter. As the doped adhesive is compressed and cured, it is heated and squeezed between the surfaces to be bonded with sufficient uniform pressure that a single layer of the conductive beads makes contact with both surfaces to be bonded. In this way, the thickness of the adhesive layer between the bonded surfaces becomes approximately equal to the size of the conductive beads. The cured adhesive film may conduct electricity via the contacting beads axially, i.e. in a direction normal to the bonded surfaces, since each bead is forced to contact both of the surfaces to be bonded. However, the cured adhesive film may not conduct electricity parallel to the bonded surfaces, since the beads may not touch each other laterally—hence the term “anisotropic”.
Prior to HSA assembly, HGAs are typically tested for acceptable function. For example, the HGAs may undergo so-called dynamic electrical testing (DET) to ensure acceptable function (and/or to characterize HGA performance for subsequent optimization or compensation in the HSA and/or in the assembled disk drive). Such testing may require a reliable electrical ground connection to the HSA. In some cases, the flexure tail may include an extra length with enlarged testing pads that include a ground pad for testing. However, such extra length must be cut-away as an extra processing step before or during HSA assembly, and the ground pad is therefore not part of the assembled HSA or the assembled disk drive.
Hence, there is a need in the art for a head suspension assembly flexure tail design that can provide a reliable ground connection, without the need for an extra length (e.g. with enlarged testing pads) that must be cut away as an extra processing step before or during HSA assembly.